You still may see some of them again if you're travelling at all, most airline staff I know change shifts quarterly (I know nothing of FAs), so they may change positions and you might be seeing lots of them again. I'm also surprised you're getting the same GAs, I get on the same flight out of YVR every couple of weeks and it's a different agent lots of the time. That said if you have any attachment to these people just be friendly, tell them you appreciate the efforts and you've written a comment card (or whatever the equivalent) and if you wanna be really nice get them a gift card, but make it for something in the airport. As a former airport employee, you grow to hate the food offered but you still eat/drink it. If you're in Canada, Timmy's or Starbucks is always a good choice in case they hate the food options, most people will drink a coffee for sure.